Display devices are mainly classified into light emitting display devices which emit light by itself, such as an organic light emitting display device and a plasma display device; and light receiving display devices which do not emit light by itself and require a light source, such as a liquid crystal display device. A general liquid crystal display device includes two display plates provided with electric field generating electrodes, and a liquid crystal layer disposed between the display plates and having a dielectric constant anisotropy. In the liquid crystal display device, an electric voltage is applied to the electric field generating electrodes to generate an electric field in the liquid crystal layer, the electric voltage is changed to adjust the intensity of the electric field to thereby form a light valve, and the transmittance of light to be transmitted through the liquid crystal layer is adjusted, whereby an intended image is obtained. Generally, an artificial light source as an additional element is used as the light source in the above arrangement. It is often the case that a fluorescent lamp such as a cold cathode fluorescent lamp (CCFL) is used as a light source, in a liquid crystal display device, for uniformly irradiating light onto the entirety of a liquid crystal panel at a rear surface of the liquid crystal panel. Normally and generally, light of a fluorescent lamp which is incident from a side surface of a light guiding plate irradiates a liquid crystal panel from a rear surface thereof, as substantially uniform light through a front surface of the light guiding plate.
In recent years, there has been developed an image display device incorporated with a light emitting diode (LED) or a laser device, as a light source free of mercury and having less electric power consumption, considering environmental issues and in the aspect of electric power saving. In particular, a laser device is said to be an optimum light source for an image display device, in the aspect of image quality such as a broad color reproducing area as well as its low electric power consumption, if used as a light source for an image display device.
Further, several methods are proposed in uniformly irradiating light onto the entirety of a liquid crystal panel at a rear surface of the liquid crystal panel, using a laser device as a light source. One of the methods is a method for scanning a liquid crystal panel by a polygonal scanner, as recited in patent literature 1. Another method is a method for scanning a liquid crystal panel by a line scanner, as recited in patent literature 2.
In the scanning method using a polygonal scanner as recited in patent literature 1, since the distance from a surface of the polygonal scanner to the liquid crystal panel is long, it is fundamentally difficult to reduce the thickness of the device as achieved in the arrangement of using a CCFL or a like device as a light source. In the method for scanning a liquid crystal panel with a line scanner, as recited in patent literature 2, it is fundamentally difficult to scan a large screen at a high speed. Accordingly, it may be practically infeasible to apply the latter method to a display device. As described above, heretofore, there has not been proposed an idea of reducing the thickness of a liquid crystal display device in backside irradiation of a liquid crystal panel using a laser device as a light source.    Patent literature 1: Japanese Unexamined Patent Publication No. Hei 2-157790    Patent literature 2: Japanese Patent No. 3205478